Patent GB-394692-A (GB)
Title: Manufacture of carbocyanine dyes
IPC: C09B23/06
Filed: 1931-12-31
Abstract: Thiocarbocyanine dyes for sensitizing photographic emulsions are prepared by condensing a 1-methylbenzthiazole quaternary salt with a trialkyl ortho-ester of a carboxylic acid, the acid corresponding with which is an aliphatic acid containing more than two carbon atoms in the molecule, or a substituted aliphatic carboxylic acid or an aromatic carboxylic acid or a substituted aromatic carboxylic acid. The benzene nucleus may contain one or more substituents, and suitable ortho-esters of carboxylic acids are trimethyl-orthopropionate, methyldiethylortho-n-caproate, methyldiethylorthoisocaproate, trimethyl-orthovalerate, trimethyl-ortho-g  - phenoxybutyrate, trimethyl-orthophenylacetate, trimethyl-orthobenzoate, and trimethyl-ortho-p-toluate.  Reaction may be carried out in boiling pyridine and it is advantageous to use a 1-methylbenzothiazole quaternary salt containing an acid radicle such as p-toluenesulphonate; the dye may then be isolated by double decomposition with ammonium bromide &c.  In examples, the following dyes are prepared by condensing the appropriate 1-methylbenzthiazole-methyl- or ethyl-p-toluenesulphonate with the appropriate ortho-ester of a carboxylic acid and decomposing the product by means of an alkali bromide or iodide: -2 : 2<1> : 8-triethylthiocarbocyanine iodide (also prepared from 1-methylbenzthiazole ethiodide directly), 2 : 2<1>-dimethyl-8-ethylthiocarbocyanine bromide, 5 : 5<1> dimethyl - 2 : 2<1> : 8<1> - triethylthiocarbocyanine iodide, 2 : 2<1>-dimethyl-(and-diethyl-)-8-n-butylthiocarbocyanine iodide, 2 : 2<1>-dimethyl-(and -diethyl-)-8-n-amylthiocarbocyanine iodide, 2:2<1>-dimethyl - 8 - isoamylthiocarbocyanine iodide, 2 : 2<1> - dimethyl- (and-diethyl-) - 8 - benzylthiocarbocyanine iodide, 2 : 2<1> : 5 : 5<1>-tetramethyl-8-benzylthiocarbocyanine bromide, 2 : 2<1>-dimethyl - 8 - g  - phenoxypropylthiocarbocyanine bromide, 2 : 2<1> -diethyl - 8 - g  - phenoxypropylthiocarbocyanine iodide, 2 : 2<1>-dimethyl-(and diethyl-)-8-phenylthiocarbocyanine bromide, 2 : 2<1> : 5 : 5<1> - tetramethyl - 8 - phenylthiocarbocyanine bromide and 2 : 2<1>-di-ethyl-8-p-totylthiocarbocyanine iodide; in the case of the latter product a mixture of products is first obtained, separation being effected by extraction with methyl alcohol.  The anion acid radicle of the dyes may also be alkylosulphate, nitrate, acetate, perchlorate or other anion that will not adversely affect the solubility or the sensitizing properties of the dye. Specifications 359,463, 378,455, 378,885, 385,267, and 385,320 are referred to.  1-Methylbenzthiazoles may be prepared by conversion of the acetyl compound of an aromatic amine into the thioacetyl compound by means of phosphorus pentasulphide and oxidation of this product with cold aqueous alkali ferricyanide.  The quaternary salts of the bases so obtained are prepared in the customary manner. Orthocarboxylic acid esters employed in the process are prepared by passing dry hydrochloric acid gas into the acid nitrile dissolved in a dry ether-alcohol mixture and reacting the resulting imino-ether hydrochloride, after separation and drying, with more dry alcohol. The Specification as open to inspection under Sect. 91 comprises the production of dyes by treating a compound containing a heterocyclic ring of the type <FORM:0394692/IV/1> as described above, and includes the condensation of benzthiazole compounds which may be substituted in the benzene ring by a fused-on benzene nucleus.  This subject-matter does not appear in the Specification as accepted.